Balanced circuit for radio apparatus



p 8,1953 N. B. THARP' 2,651,685

BALANCED CIRCUIT FOR RADIO APPARATUS Filed July 14, 1948 1.? .10 J1 1512 Load I L Inductance- .Dgbw 21 22 51516 p d 1 Vail-a a no e 20 5446/ 117 18 1 012"; e

500x25 g. g Sup/1 y L Jource Load 51 .[nduczance Bias 51;;0! I It 0- age$055; p/ y Source Source *3 WITNESSES; INVENTOR Nelson 5. Tkaqb.

Patented Sept. 8, 1953 BALANCED CIRCUIT FOR IRA-D10 APPARATUS- Nelson B.Tha'rmElli'cott City;

Md, assign or" to Westinghouse Electric Corporation, East Pittsblifgfi,Pit a Coil 501 3115011 f PeifllS'Yl-vfiliifl;

Application July 14, 1948, Serial No. 38,696

i This invention relates to vacuum tube circuits,

and" itrelates more particularly to circuits for automaticallyequalizing the grid'and anode cur-- rentsot vacuum tubes working into acommon load.

' In order to increase the power handling capacity of vacuum tubes,- itis common practice to connect them in parallel, push-pull, or push pullparallel, in order that two or more" tubes can work into a common load;When tubes are so connected, differences in their characteristics or inthe'characteristicsot their circuit components may cause one tube todraw" morefano'de current than another tube. Likewise, when the tubesare-so operated as to draw grid current, one tubemay draw more gridcurrent than another tube.

This invention provides a balancing circuit which will automaticallybalance" the grid cur-- rents and the anode currents of vacuum tubesworking into a common load.

An object of the invention is'to' b'alanc'e'au'to matically the anodecurrents of vacuum tubes working'into a common load.

Anotherobject of the invention is to balance automatically the gridcurrents of'vacuumtubes working into a common load. I I

The invention will now be described with reference to the drawing ofwhich:

Fig. 1 is a circuit schematic illustrating one embodiment of theinvention as used with paral lel-connected vacuum tubes, and

Fig. 2 is a-circuit schematic illustratinganother embodiment of theinvention as used'with pushpull-connected vacuum tubes. I

Referring first to Fig. l, the tubes I0, II- and I2 have their anodesconnected together and to one end ofthe load inductance I3, the otherend of which is connected to the positive terminal of the anode voltagesupply source I4, the negative terminal of which is grounded. The gridsof the tubes are connected together and through the coupling condenserI5- to'an input circuit.

The cathode of the tube I0- is connected to ground through the cathodebias resistor I6=; the'cathode of the tube I I is connected to groundthrough the cathode bias resistor I1, and the cathode of the tube I2 isconnected to ground through the cathode bias resistor l8.

The resistor I9 is connected to the cathode of the tube I0 and to thepositive terminal of the bias voltage supply source 20, the negativeterminal of which is connected through the grid resistor 2| to the gridsof the tubes II], II, and I2. The cathode of the tube II is connected 6oiaim's.- (01. 179 171) through the resistor 22 to the positiveterminal" of the source 20, and the cathode of the tube I2 is connectedthrough the resistor 23 to the positive terminal ofthe source 20.

The values of the resistors I6, I 1, and I 8 should be less than thevalues of the resistors I9, 22, and 23', so that the normal flow of thecathode currents is through the resistors I6, I1, and I8. In theoperation of the embodiment of the invention illustrated by Fig. 1, ifthe tubes are operated so as to draw grid current, then if the gridcurrent'o'f the tube I0 increases, this will cause an increased voltagedrop through the resistor I9 which will cause the grid of the tube to bebiasedmorenegatively with respect to its cathode, thus decreasing thegrid current. Likewise, if the grid currents of the tubes II and I2increase, the increased voltage drops through the resistors 22 and 23will cause the grids of the tubes I I and I 2' tobe biased morenegatively with respect to their cathodes, thus causing them to drawless grid current.

Regardless of whether or not the tubes draw grid current, if the anodecurrent of the tube I0 increases without a corresponding increase in theanode currents ofthe tubes and I2, the voltage drop across the resistorI6 will increase, causing the cathode of the tube It to become morepositive than the cathode of the tubes II' and I2, with the result thatthere will be'a current flow between the cathodes through the resistorsI9; 22, and 23. The resulting voltage drop through these resistors addsto the negative bias on the grid of the tube I0, and subtracts from thenegative bias on the grids of the tubes II and I2. This will result inthe tube I0 drawing less anode current, andin the tubes II and I2drawing more anode current, thus balancing the load" on the tubes.Likewise, if the anode current of either of the tubes I I' or I2increases without a corresponding increase in the anode current of theother tubes, the cathode of. the tube with the increased current flowwill become more positive, resulting in the flow of current between itand the cathodes of the other tubes;resulting in the tube drawing thegreatest anode current having its grid biased more negatively, andresulting in the grids of the other tubes being biased more positively,with the result that the loads on the tubes are balanced.

In the embodiment of the invention illustrated by Fig. 2, the tubes 29and 30 are connected in push-pull with their anodes connected to theopposite ends of the load inductance 3|, the center point of which isconnected to the positive terminal of the anode voltage supply source32, the negative terminal of which is grounded.

The cathode of the tube 29 is connected through the cathode resistor 33to ground. The cathode of the tube 30 is connected through the cathodebias resistor 34 to ground. The resistors 25 and 26 are connected inseries and. to the cathodes of the tubes 29 and 30, and their midpointconnection is connected through the re-.

sister 21 to the positive terminal of the bias voltage supply source 28.The grid resistors 39 and 40 are connected in series and to the grids ofthe tubes 29 and 30, and their mid-point connection is connected to thenegative terminal of the source 28.

The input signal is applied through. the coupling condensers 4| and 42to the grids, of the tubes 29 and 3B.

The values of the resistors 33 and 34 should be less than the values ofthe resistors 25 and 25, so that. the. normal. how of. the cathodecurrent. isthrough theresistors 33 and 34.

In the operation of the embodiment of the in.- vention illustrated. byFig. 2-, ii the tubes are operated to draw grid current, and if the tube29 draws more. grid current than the tube.- 33, the. increased voltage.drop through the resistor 25 will cause the grid of the tube 29. to bebiased more negatively with respect to its cathode, thus decreasing thegrid current. grid current of. the tube 3D increases, the increasedvoltage drop through the resistor 2% will cause. the grid of. the tube381 to be biased more negatively with respect. to its. cathode, thus.decreasing the flow of. gridcurrent.

Regardless. of whether or not the tubes 28 and 3B draw grid current, ifthe anode current. of the tube 2Q increases without av correspondingincrease. in the anode current of the tube 3!), the voltage drop. acrossthe resistor 33 will increase, causing the cathode of. the tube 29- tobecome more positive than the cathode of. the tube 33, with the. resultthat there will be. a flow of current. through the resistors 25 and 23.The resulting voltage drops through these resistors add to the negativebias to the grid of the tube 29 and subtract from the. negative bias onthe grid of. the tube 3! resulting in the tube 2'3 drawing less. anode.current and resulting in the tube 38' drawing more. anode current, sothat the load. on the two. tubes tends to balance. In the same way, ifthe. tube. 3.6. draws more anode current than the tube 2.9,. the flow ofcathode current through the resistors 25 and 25 will result in the gridof the. tube 351 being biased more negatively, and will. result in thegrid. of the tube 29' being. biased more positively, so that the anodecurrents tend to balance.

The; load inductances connected in the" anode circuits of the tubes maybe the primary wind.- i'ngs of output transformers or may be tank coils,or other forms ofloads.

Each of the push-pull-connected tubes 29 and 30 of Fig. 2 may have othertubes connectedin parallel with it, as illustratedby Fig. l.

I claim as my invention:

1. An electrical system comprising a plurality of vacuum tubes having atleast controlgrids,

Likewise, if the.

cathodes, and anodes; an anode voltage supply source; an output loadcircuit for said tubes; means connecting the anodes of said tubesthrough said load circuit to the positive terminal of said source; anindependent bias voltage supply source having its negative terminalconnected. to the control grids oi said tubes; resistors connecting saidcathodes tov the positive terminal of said bias voltage supply source,bias resistors connecting said cathodes to the negative terminal of saidanode voltage supply source, and an input. circuit connected to saidgrids.

2. An electrical system comprising a plurality of. vacuum. tubes havinginterconnected control grids andinterconnected anodes, and havingcathodes; an anode voltage supply source; an output load circuit; meansconnecting said anodes through said load circuit to the positiveterminal of said supply source; an independent bias voltage supplysource having its negative terminal connected to said control grids;resistors connecting said: cathodes to the positive terminal of saidbias voltage supply source, bias resistors connecting said cathodes tothe negative terminal of said anode voltage supply source, and. an inputcircuit connected to said grids.

3.. An electrical system comprising a pair of vacuum tubes. havingcontrol grids, cathodes; and anodes; an input circuit connected pushpullto said grids; a load circuit connected pushpull to said anodes; ananode voltage supply source. having its positive terminal connectedthrough said load circuit to said anodes; gri'd' resistors connected inseries between said control grids; a bias voltage supply source havingits negative terminal connected to the mid-point connection of saidresistors; other resistors connected in series between said cathodes,the positive terminal of the latter said source being connected to themid-point connection of said other resistors, and bias resistorsconnected in series between. said cathodes and having their midpointconnection connected to the negative terminal of said anode voltagesupply source, there being no fixed electrical relationship between thenegative. terminal of the bias voltage supply source and the negativeterminal of the anode voltage supply source.

4. The electrical system of claim 2-, in which said control grids aredirectly connected to gether.

5. The electrical system of claim 2, in which said anodes are directlyconnected, together.

6,. The. electrical system of claim 2, in which said control grids aredirectly connected" together, and said. anodes are directly connectedtogether.

NELSON B THARP;

References. Cited in the file of this patent UNITED STATES PATENTSNumber Name Date 1,973,725 Ranger Sept. 18, 1934 2,123,241 Harley July12,. 193% 2,337,918 Moyer Dec. 28, 1943 2,416,188 Mcle1lan Feb. 18, 1947

